Ferrite switching apparatus



Dec. 15, 1959 w. .1. PARRIS 2,917,679

' FERRITE SWITCHING APPARATUS Filed June 5, 1957 F lg. I.

ISDJ- 20 i T Pulse E Generator T 6 I L 1 l8 Fig. 2

WITNESSES: INVENTOR" @W m9fi2.(;- William J. Porris B BY 44 ,21

ATTORNEY smr mnmarmrus William J. Parris, Harundale, Md assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a

corporation of Pennsylvania Applicationjune 5, l95 7 s,e, ji,al No. 663,827

8 Claims. ((11. 317.123)

This invention relates .to a ferrite switching method ,and apparatus, and more particularly to a method and apparatus for operating a ferrite switch while maintaina minimum power consumption.

A ferrite switch usually consists of acoil wound as a solenoid on or in a section of longitudinally slotted cirsa uave uid hi h s 220d ts it positioned n -it water n As will be readily understood by :those skilled in the art, subjecting the ferrite rod to an magnetic field may change the attenuation causedby the ferrite rod and may also result in shifts in the phase and polarization of the energy in the waveguide. To actuate the switch, it is necessary to introduce a current of proper amplitude into the coil. Removal of the current de- The tin e required for the current tobuild up or decay from the required value is the switch- ,ing time. Usually, there is a resistor inserted in series with the coil and the current flowing in the resistor represents a power loss of considerable proportions.

The apparatus and method of the instant invention ,ppovide for the operation of a ferrite switch with a minimum of power consumption. This is accomplished by inserting in series with the coil and the source of energization a resistor having a predetermined value which is equal to the surge or characteristic impedance of the coil when considered as a delay line, and applying to the series combination a pulse of preselected amplitude, shape and duration.

Accordingly, one of the primary objects of the invention is to provide new and improved ferrite switching appa atusa 'A second object is to provide a new and improved method for pulsing the coil of a ferrite switch.

Another object is to provide new and improved ferriteswitching apparatus requiring a minimum of power to operate the same.

A further object is to provide a new and improved method for reducing the power required to operate a ferrite switch. 7

Other objects and advantages will become apparent aftera perusal of the following specification when studied in connection with the accompanying drawings, in Which? Figure 1 is a schematic electrical circuit diagram of prior art ferrite switching apparatus and is included to .ass-istin: illustratingand describing the improvement pro- -vided by the instant inventiongand Fig. 2 is a schematic electrical. circuit diagram of ap paratus constructed according to the preferred embodiment of the instant invention, and further illustrating the method of pulsing the coil of the ferrite switch.

.Particular reference should be made now to the drawings for a more complete understanding of the invention .and in particular to Fig. 1 thereof. The coil 9 illustrates a. conventional solenoid having associated therewith the --ferrite member ltl-of a ferrite-switch. vOne terminal of the coil;9. is conneoted'byway of'r'esistor 11 to one power input terminal 12, whereas the other terminal of coil 9 U e SW Patent '0 2,917,679 Patent fi Dec. 15, 1959 e l C is connected to-anadditionalpower input terminal '13,

terminals 12 and 13 having appliedthereto from means,

where L is the inductance of the coil .9, R is .the series resistance of resistor 11, and E is the amplitude of v the applied voltage pulse 14. Following the end of ,the voltage pulse, the current -will, decay ,according to the formula 1 R t "thfi e The current is the value required ,tooperatethe switch, that is, the value required to set up a magnetic field of the required strength in the ferrite member. The switching time is the time required for the current .in the coil to rise to 99% of this valueordecay to approximately 5% of this value. It will be noted tha;t..even for small values of coil inductance a large series resistance at 11 will be required for. rapid switching, with ,a corresponding large pulse amplitude. Thissituation leads to excessive power requirements for the operation of the switch. The distributed capacity :ofthe coil ,9 ,and. the stray capacity to ground will cause undesirable oscillations in the current in the coil. No satisfactory'rnethod of decreasing these capacities has been found without leading to further difficulties.

Particular reference should be made now to Fig. 2 which shows the preferred embodiment of the apparatus of the instant invention. In the apparatus of Fig. 2, for a given switching time, the value of the non-inductive series resistor 16 may be reduced considerably from the value of the series resistor 11 of Fig. 1. The stray and distributed capacities of the ferrite switch coil are put to use in the apparatus of Fig. 2. The capacity C and the inductance L of the solenoid coil 15 of Fig. 2 form the elements of a distributed constant delay line of surge impedance Z, and time delay T. .Coil 15 and resistor 16 are connected to terminals 17 and 18 which have connected thereto to energize the coil a source of pulses 19 for. providing a pulse 20 having an amplitude E. The

time required for the current in coil 15 to build up to E is T. This same time is required for the current to decay to-zero amplitude after the pulse ends.

The characteristic or surge impedance of the delay line comprising coil 15 is given byv the formula where L is the inductance of the coil 15 and C is the distributed capacity. As aforementioned, the resistor 16 has .a preselected value R determined by the formula R=Z The aforementioned time T is given by the formula duces the value of the series resistance considerably from that shown in Fig. l with a proportional saving in the power lost in the resistor.

The pulse 20 generated by generator 19 and applied to the series combination of inductor 15 and resistor 16 by way of terminals 17 and 18 preferably has an amplitude E=Ri where i is the coil current required to set up the necessary magnetic field strength, and a pulse duration corresponding to T plus the length of time it is desired to have the ferrite switch operated.

The application of a switching pulse of this preselected amplitude and duration maintains at a minimum the power consumed by the ferrite switch.

As will be readily understood by those skilled in the art, even where a slotted waveguide is used, considerable power is consumed at the beginning of the pulse in setting up eddy currents in the waveguide walls. If desired, generator 19 may supply a peaked pulse in which the leading edge is spiked, to assist in overcoming circulating current effects in the Waveguide walls and to provide for losses occurring the ferrite material.

Accordingly, there has been shown and described a method and apparatus admirably suited to accomplish the aforedescribed objects of the invention.

Whereas, the invention has been shown and described with reference to a preferred embodiment thereof which gievs satisfactory results, it should be understood that changes may be made and equivalents substituted without departing from the spirit and scope of the invention.

1 claim as my invention:

1. In combination with a switch coil connected in circuit as a delay line and to have set up therein a magnetic field having a predetermined magnitude needed to operate the switch within a predetermined time while maintaining the power consumed in setting up and maintaining said field at its minimum value, a non-inductive resistor connected in series with said switch coil, said resistor having a value of resistance R substantially equal to the surge impedance Z of the delay line, where L being the inductance of the coil and C the distributed capacity, and means for applying to the series circuit including the coil and resistor a pulse having an amplitude E RI, where I is substantially the instantaneous coil current required for setting up the magnetic field needed to operate the switch, the pulse having a time duration T=T +T T corresponding to the time required for the current in the coil to build up to said required value and calculated according to the formula T =\/LC, and T corresponding to the time duration said field is to be maintained.

2. Ferrite switching apparatus comprising, in combination, circuit means including a coil connected in circuit as a delay line and adapted to be disposed in predetermined relation to a ferrite member to, when energized, set up a magnetic field in said member having a predetermined magnitude needed to operate the switch, a non-inductive resistor connected in said circuit means in series with said coil, said resistor having a value of resistance R substantially equal to the surge impedance Z, of the delay line, where L being the inductance of the coil and C the distributed capacity, and pulse generator means connected to the circuit means including the coil and resistor and supplying thereto a pulse having an amplitude E=RI, where I- is substantially the instantaneous coil current required to set up the magnetic field needed to operate the switch, said pulse having a preselected time duration at least equal to V16, the delay time of the delay line.

3. Ferrite switching apparatus comprising, in combination, circuit means including a coil connected in circuit as a delay line and adapted to be disposed in predetermined relation to a ferrite member to, while energized, set up within a predetermined time a magnetic field in said member having a predetermined magnitude and maintain said field, a non-inductive resistor connected in said circuit means in series with said coil, said resistor having a value of resistance R substantially equal to the surge impedance Z, of the delay line, where L being the inductance of the coil and C the distributed capacity, and pulse generator means connected to the circuit means including the coil and resistor and supplying thereto a pulse having an amplitude E=Rl, where I is substantially the coil current required to set up said magnetic field, said pulse having a preselected time duration T =T +T T corresponding to the time required for the current in said coil to build up to said required value according to the formula T /LC, and T corresponding to the time duration said magnetic field is to be maintained.

4. In combination, a circuit having a pair of input terminals, a switch coil having a selected inductance value L and a selected distributed capacity value C and being c0nnected as a delay line in said circuit, resistance means terminating the delay line with a resistance value R substantially equal to and means for supplying to the pair of input terminals a pulse having a preselected amplitude E, where E=RI, and I is the instantaneous current in said coil required to set up a magnetic field of the necessary magnitude to effect the switching operation.

5. In combination, a switch coil, a circuit having a pair of input terminals to set up within said coil Within a time T a magnetic field of the required magnitude to operate the switch coil, said switch coil having a selected inductance value L and a selected distributed capacity value C and being connected as a delay line in said circuit, resistance means terminating the delay line with a resistance value R substantially equal to and means for applying to the pair of input terminals a pulse having a predetermined duration at least equal to said time T and a preselected amplitude E, where E=RI, and I is the instantaneous current in said coil required to set up a magnetic field of the necessary magnitude to effect the switching operation, the time T being substantially equal to the delay time of the delay line according to the formula I: V ITC 6. In combination, a switch of the type employing a coil to set up a magnetic field to effect the switching operation, said switch having a required switching time T, said coil having an inductance value L and a distributed capacity value C which provide a delay time T for the coil while connected in circuit as a delay line, resistance means terminating the delay line with a resistance value R substantially equal to and means for applying across the series connected coil and resistance means a pulse having a predetermined duration at least equal to T and a predetermined amplitude E, where E RI, and I is the instantaneous current in said coil required to set up a magnetic field of the necessary magnitude to effect the switching operation.

7. In ferrite switching apparatus including a ferrite member, in combination, a pair of input terminals, a coil disposed in predetermined position with respect to said ferrite member and adapted when energized to set up a magnetic field in said ferrite member, said coil having a selected inductance value L and a selected distributed capacity value C, and circuit means connecting said coil as a delay line to said pair of input terminals, said circuit means including impedance means which is substantially a pure resistance terminating said delay line, said impedance means having a resistance value said pair of input terminals being adapted to have applied thereto a pulse having an amplitude E=Rl, where I is the instantaneous current in said coil required to set up a magnetic field of suflicient magnitude to effect the switching operation, said pulse having a time duration at least equal to Via the delay time of the delay line.

8. In ferrite switching apparatus including a ferrite member, in combination, a switching pulse generator for providing pulses of predetermined amplitude, a coil disposed in predetermined position with respect to said ferrite member and adapted when energized to set up a magnetic field in said ferrite member, said coil having a selected inductance value L and a selected distributed capacity value C, and circuit means connecting said coil as a delay line to said pulse generator to have switching pulses applied thereto, said circuit means including impedance means which is substantially a pure resistance terminating said delay line, said impedance means having a resistance value References Cited in the file of this patent UNITED STATES PATENTS 2,719,274 Fuhrs Sept. 27, 1955 2,745,069 Hewitt May 8, 1956 2,798,205 Hogan July 2, 1957 

